This invention relates to a drum unwind system for sheet materials in roll form such as rolls of paper, tape and the like.
Drum unwinds for the unwinding of rolls of sheet material commonly include a hard surfaced unwind drum such as a metal drum. The drum for the purpose of effecting the unwinding of the sheet material is placed against the periphery of the roll of sheet material so that a pressure nip between the peripheries of the drum and the roll is formed. Also, the roll of sheet material is mounted to be free to rotate and the drum drives the roll in rotation through the pressure existing in the nip between the drum and roll. As the unwinding of the roll takes place, the sheet material is drawn from the nip and is passed to other devices such as reels, forming boards and the like.
The pressure in the nip between the rolls as the diameter of the roll of material decreases is maintained in any convenient manner as by use of the air cylinders. For this purpose, of course, either the roll of material or the drum is mounted to be moved transversely of its axis by the action of the air cylinders.
The mentioned unwind system of the prior art is useful but suffers from certain drawbacks. A first of these is that commonly the roll of sheet material termed, for convenience, the parent roll is more subject to deformation radially than is the unwind drum. This leads to a condition in which the lineal speed of the parent roll in the pressure nip differs from the surface speed of the remainder of the roll.
Stated somewhat differently, the diameter of the parent roll as measured from the nip radially is less than the diameter of the parent roll and all other undeformed portions of the roll. A sag in the material being unwound then occurs. The difficulty mentioned is particularly apparent with sheets of material which are of low stretch and/or are of low strength.
A primary purpose of the present invention is to provide a novel method for the unwinding of rolls of sheet material utilizing an unwind drum system in which the unwind drum has a surface of a material which deforms much more easily than the roll of material to be unwound.
An important object of the invention is to provide a drum unwind system in which the unwind drum has a covering of a very soft deformable foam material. A further object of the invention is to describe novel apparatus arrangement for unwinding sheet material.